1. Field of the Invention
The present invention relates to air intake filters for internal combustion engines, and, more particularly, to an air intake filter for an internal combustion engine which is designed to prevent the escape of fuel fumes as atmospheric pollutants.
2. Description of the Prior Art
Unburned fuel escaping to the atmosphere in the form of fumes from the fuel supply system of automotive internal combustion engines at standstill is a source of air pollution. A continuous slow discharge of fuel fumes takes place at the fuel tank and a considerable discharge of fumes takes place through the fuel control system and the air intake filter of a hot engine, immediately after shutdown of the engine.
It has already been suggested to prevent these discharges of fuel fumes to the atmosphere by controlling the fumes in such a way that they have to pass through a bed of activated carbon which precipitates and absorbs the fuel fumes. Advantageously, this bed of activated carbon is arranged in the air intake filter itself, so that the fuel which is collected by the activated carbon is drawn back into and consumed by the engine, as soon as it is restarted, thereby automatically regenerating the activated carbon.
For reasons of limited space, automotive internal combustion engines have air intake filters with filter cartridges of low height and comparatively large traverse dimensions. These filter cartridges are either in the shape of a large annulus around a vertical axis, or in the shape of a large plate.
An engine air intake filter with a fumes-absorbing bed of activated carbon is disclosed in the German Offenlegungsschrift (Publ. Appln.) No. 19 27 046, where the air intake filter has an annular filter cartridge with vertical fold edges between which the combustion air enters in a horizontal radial direction. The openings of the wedge-shaped fold cavities on the downstream side of the filter cartridge are covered by means of a fabric cover which is supported by a mesh screen. This screen-supported fabric retains a filling of activated carbon particles in the downstream fold cavities. The publication in question does not disclose how the fold cavities are closed off at their upper and lower extremities.
This prior art filter cartridge has failed to live up to its expectations over extended periods of use. The inevitable presence of vibrations and shocks leads to a settling and packing of the activated carbon in the lower portions of the fold cavities, thereby creating an open flow space above the compacted bed of activated carbon. By thus permitting the fuel fumes to bypass the activated carbon, this prior art filter cartridge largely defeats its purpose. An additional shortcoming of the prior art filter relates to the fact that the assembly of the filter cartridge, especially the introduction of the activated carbon, is somewhat difficult. On the one hand, it is necessary, for the reasons just stated, to fill the fold cavities as completely as possible, on the other hand, the particular configuration of the filter cartridge requires rigid closure members at the axial extremities of the fold cavities, so that the fold cavities must not be over-filled.